Apparatus for compressing thermoplastic masses



Allg 21, 1951 R. COLOMBO 2,564,880

APPARATUS FOR COMPRESSING THERMOPLASTIC MASSES Filed Feb. 19, 1948 v FQl.

. INVENTOR alvcirv 67020122170 Patented ug. 21,; 1951 UNITED STATESPATENT OFFICE.

APPARATUS FOR COMPRESSING THERLMTPLASTIC lMASSES Roberto Colombo, Turin,Italy Section 1, Public Law 690, August 8, 1946 Patent expires February15, 1964 3 Claims. Al

This invention relates to an apparatus for the compression of plasticmasses more particularly in extrusion presses.

It is well known that many synthetic resins, before they can be reducedto articles of manufacture, are in a pulverulent condition and have avery low apparent specific weight. In order to utilise them, either inthe form of pressing powders or for the manufacture of proled articlesit is necessary previously to incorporate therein softening,plasticizing agents, or pigments, filling substances and so on. It istherefore necessary thoroughly to mix these synthetic resins, .generallyat a temperature over 100 C. and 'under a high pressure, in order to mixthe raw materials with the auxiliary ingredients. The methods employedheretofore for this preliminary treatment of plastic masses are basedupon the use of solvents, mixers and, finally, extrusion presses.

This invention relates to a device of the latter class which affords thefollowing advantages over those employed heretofore:

1. Thorough mixing of the ingredients,

2. Strong power of reduction of the specific volume from the initialpulverulent to the final compact state,

3. Production of very high pressures at the outlet of the material,

4. Extreme simplicity of the apparatus which is strong and inexpensive,easily cleaned, which is important when colours of type of materialunder treatment when going over from one colour of type of materialunder treatment to another,

5. Large output with inexpensive means.

It is essential to fulfill all these requirements for obtaining articlesof manufacture of constant quality and having the best properties.

The apparatus comprises a central body of conical spiral shape, which ismoved eccentrically and parallel to itself within a chamber in the shapeof a conical screw. The movement performed by the central body is only acircular movement of its axis parallel to itself, so as to displace theturns of the conical spiral of the inner element within the turns of theconical spiral of the stationary outer element, thereby graduallydisplacing the line of contact of the various turns over the fullquadrant. As the diameter on each turn of the inner element is smallerthan the diameter on the corresponding turn of the outer element, achamber is formed between the two turns in which, by effect of the abovedescribed movement, the material is rapidly pushed forward as it isstrongly compressed through the correspondingly rapid reduction involume of the chamber confined by one turn with respect to the volume ofthe chamber limited by the preceding turn. The pitch of both spirals,the inner and outer one, is of course the same. Moreover, theabove-mentioned difference in diameter between the cooperating turns ofthe two inner and outer elements has to be twice the eccentricity of themovement performed by the inner element. The material which has beenadmitted in a pulverulent condition through the inlet situated near thelargest diameter of the outer element, will issue in a thoroughly mixedand considerably compressed condition through the outlet near the frontend at which the inner and outer conical spirals abut. The desiredcompression is of course determined by the axial extent of the steps ofthe helices and the output of the machine by the pitch of the spiral. Abaclrflow of material from the outlet towards the inlet is impossible,since each turn of the inner element contacts along a line parallel tothe axis of said inner element with the corresponding turn cf the outerelement. When it is desired to compress the material to a still higherdegree, the inner and outer conical spirals are given a pitch graduallydecreasing from the inlet towards the outlet end.

When high compressions are not required, but it is desirable to convey alarge quantity of material under a relatively low pressure, the pitch ofthe spiral may increase from the inlet towards the outlet, therebygradually increasing the section of the chamber between the two screws.

The apparatus is either heated or cooled, depending upon the nature ofthe material treated.

The accompanying drawing shows by way of example one particularconstruction of apparatus according to the invention.

Figure 1 is an axial view of the inner conical helix;

Figure 2 is an axial section of the outer conical helix;

Figure 3 is a sectional View of the assembled apparatus with the membersadapted to impart the above described movement to the inner and outerelement, respectively.

Fig. 4 is a partial section of Fig. 3 on line IV-IV.

Referring to these drawings l denotes the inner conical helix and 2 theouter casing of the apparatus in which the outer conical helix 3 isformed, having on each winding the same pitch as the inner helix I, butof a larger diameter, the difference 3a between the two diameters beingtwice the eccentricity of the movement of the element I with respect tothe element 2. 1n Figure 3, the inner helix I is in the position inwhich its turns are in contact with those of the outer helix 2 along astepped line (shown underneath the axis in the section plane in whichthe gure is drawn) whilst in the diametrically opposed position there isthe largest section of the chamber C formed between the turns of the twoelements I and 2; the inner element I has a journal 4 the axis of whichis indicated by X--X and on which the worm wheelV with an eccentric axisY-Y is mounted through a co-axial bushing 5, and receives motion throughan endless screw 1, Figi 4. The worm screw 6 is guided through theinterposition of rollers 8 on the rings 9 and the axial thrust issupported by the disc I with the interposition of balls I I. Due to theeccentricity of the worm wheel 6 and its annular supports II withrespect to the journal 4 on which said wheel is mounted, a movementparallel to itself is imparted to the journal 4, resulting in thedisplacement of its axis X-X about the axis Y-Y which brings about asimilar movement of the inner conical helixfrI with respect to theelement 2. The material is fed into the inlet I2 and discharged throughthe drawing-die I3 formed in the casing 2 in its front portion, stronglycompressed because of the rapid reduction of the helical chamber throughwhich it is fed. The apparatus is of extreme simplicity, since itconsists of only three parts which are of simple construction and easilydis-assembled.

The constructiona1 details of the apparatus may be varied from theexample shown and described, without departing from the scope o thisinvention.

What I claim is:

l. Apparatus for mixing and compressing plastic masses, comprising aninner spiral member mountedV on a cylindrical journal, an outer spiralmember having its turns equalling in axial extent associated turns ofsaid inner member, the diameter of the turns of the inner member dii"-fering from the diameter of the associated 'turns 45 of the outer memberby a constant value, means for holding the axis of said inner memberparallel to the axis of the outer member, means for revolving the axisof said inner member about the axis of said outer member, so that eachturn of the inner member constantly contacts along a line parallel tothe axis of said member with the associated turn of the outer member,means for preventing rotation of the inner member about its own axis,the turns of said inner member coming progressively into contact withthose of the outer member, thereby pushing forward and compressing thematerial entering at the outer periphery of the spiral of the outermember and issuing centrally at the front end thereof.

2. Apparatus for mixing and compressing plastic masses, as claimed inclaim 1 wherein the pitch of the inner and outer member graduallydecreases from the inlet towards the outlet end, in order to increasethe compression of the ma; terial;

3. Apparatus for mixing and compressing plas; tic masses, comprising anouter spiral member, a ring xed to said outer spiral member, a wormwheel mounted on said ring through the interposition of rollers, saidworm wheel being eccentrically bored, means for actuating said wormwheel, a bush in the eccentric bore in said worm wheel, a cylindricaljournal in said bush, an inner spiral member xed to said cylindricalpivot and having its turns equalling in axial extent the associatedturns of said outer member, the diameter of the turns of the innermember diiering from the diameter of the associated turns of the outermember by a constant value, each turn of the inner member constantlycontacting along a line parallel to the axis of said inner member withthe associated turn of the outer member, means for preventing rotationof the inner member about its axis.

ROBERTO COLOMBO.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,353,917 Lambert Sept. 28, 19201,904,884 Royle Apr. 18, l933 2,343,529 Brown Mar. '7, 1944

